The present invention generally relates to an improvement in the binding of phosphors to the display screen of field emission displays and, in particular, to the use of inorganic and organic binder materials that may be either conductive or semi-conductive.
Field emission display (FED) technology utilizes a matrix addressable array of pointed, thin film, cold field emission cathodes in combination with a phosphor luminescent screen, as represented, for example, by U.S. Pat. No. 5,210,472, the disclosure of which is incorporated herein by reference. An emissive flat panel display operates on the principles of cathodoluminescent phosphors excited by cold cathode field emission electrons. A faceplate having a cathodoluminescent phosphor coating, similar to that of a cathode ray tube, receives patterned electron bombardment from an opposing baseplate thereby providing a light image that can be seen by a viewer. The faceplate is separated from the base plate by a narrow vacuum gap. Arrays of electron emission sites (emitters) are typically sharp cones on the cathode that produce electron emission in the presence of an intense electric field. A positive voltage is applied to an extraction grid, relative to the sharp emitters, to provide the intense electric field required for generating cold cathode electron emission. Prior art FIG. 1 is a photocopy of FIG. 1 of the above-referenced U.S. Pat. No. 5,210,472. FIG. 1 shows a perspective view of the baseplate of a field emission display. As shown, the baseplate includes a plurality of base electrode strips 12A–12C, and a plurality of grid electrode strips 11A–11C. A plurality of field emission cathodes, or emitters, 13 are disposed on the base electrode. The tip of each emitter is surrounded by a grid strip aperture 14. In operation, voltages applied to the base electrode and the grid electrode cause selected emitters to emit electrons that travel towards a faceplate.
FEDs are less tolerant to particle shedding from the faceplate than CRTs and, thus, excellent and repeatable adhesion and faceplate integrity are required. The cathode of the field emission display is in very close proximity to the faceplate and is sensitive to any electronegative chemicals arriving on the cold cathode emitter surfaces, which could absorb them and increase the value of the emitter work function. Typically, FEDs are operated at anode voltages well below those of conventional CRTs. The material properties of the surface, distance along the surface, and changes in the orientation of the surface relative to a straight line between the two voltage nodes determine the voltage at which flashover between the cathode and faceplate occurs. Because FEDs employ lower anode voltages, phosphor material screening and the process of binding them to each other and to the faceplate have to be optimized and tightly controlled to minimize the dead layer and allow for effective excitation of the phosphor. Most phosphor lifetimes are largely determined by the total accumulated charge delivered per unit area through the life of the display.